Modern oscilloscope probes typically have either one or two inputs and can therefore measure either in a ground-referenced or differential manner. A linking of the input signals in this context takes place only in the basic device (oscilloscope) itself. Accordingly, in the measurement of several signals, several probes are also always required or respectively, with the use of a single probe, this must be re-contacted several times.
A mode-selection amplifier circuit for use in a signal registering probe is known from EP 2 022 169 B1. The mode-selection amplifier circuit in this context comprises several difference-amplifier circuits, to which three signal inputs are supplied. For the case that one of the supplied signals is a reference signal (for example, ground), with the mode-selection amplifier circuit presented, either the push-pull-mode, the common-mode or one of the corresponding ground-referenced modes can be measured. The disadvantage with EP 2 022 169 B1 is that the bandwidth is restricted because of the use of difference-amplifiers for the arithmetic combination of the input signals, and that the difference amplifiers necessarily require voltages as input signals, so that the transistors within the difference amplifiers must be designed for the full voltage range of the input signals. As a result, either the input-voltage range must be severely restricted, or it is not possible to use particularly fast transistors with a very high transit frequency, because these transistors provide a low breakdown voltage.
An object of the present invention is therefore to provide a switching unit for the arithmetic linking of several input signals and a corresponding probe which allows the use of very fast transistors in order to achieve a high bandwidth with these.